Printed electronics may be viewed as an extension of printed circuit board technology. Generally described, a printed circuit board includes a substrate with conductive metal paths for wiring. All other electronic components are made separately and are soldered or clamped to the substrate of the printed circuit board. In more recent developments, semiconductor integrated circuits are now produced to perform most electronic circuit functions. Production of integrated circuits, however, requires the use of specialized semiconductor substrates and is expensive and impractical for producing ultra low-cost electronic devices. For example, typically the cost of integrated circuits cannot be lowered significantly and even a relatively low level of cost cannot be achieved unless the integrated circuits are produced in a very high volume because of the very high cost of an integrated circuit fabrication line.
Printed electronics are formed by printing images layer by layer, i.e., by depositing one or more layers of material on a wide variety of substrates, including uncoated or coated paper, laminated paper products, various plastic films such as polyethylene or polynaphthalene, etc. With printed electronics technology, it is possible to produce microelectronic components of an electronic circuit. Some examples of microelectronic components that may be produced include transistors, capacitors, resistors, diodes, and light emitting diodes, while examples of complete circuits include RFID tags, sensors, flexible displays, etc. As an example, a capacitor can be constructed by depositing a conducting area, followed by depositing a larger insulating layer, and then another conducting area. This process can be repeated to obtain higher capacitance. As another example, a field-effect transistor can be formed by depositing a conductor layer forming source and drain electrodes, a semiconductor layer, a dielectric layer, and then another conductor layer forming a gate electrode.
Especially when low-cost conducting and semiconducting materials, such as organic polymers, are used as the materials to be deposited, printed electronics forming complete functional circuits (e.g., RFID tags) may be produced at a very low cost on the order of about one-tenth of the cost of producing analogous integrated circuits. Such low-cost printed electronics are not expected to compete directly with silicon-based integrated circuits. Rather, printed electronics circuits may be produced to offer lower performance (e.g., lower frequency, lower power, or shorter lifetime) at much lower cost as compared to silicon-based integrated circuits.
Printed electronics components are made using a set of materials, typically five to seven different materials. These are usually liquids with dissolved and/or suspended polymers, polymer precursors, inorganic materials, and organic or inorganic additives, and are deposited in a wet printing process. Typical wet printing methods include letterpress-printing, screen-printing, and ink jet printing. Specifically, these materials are deposited in a desired sequence on a substrate and are often cured or activated by a thermal cycling and/or humidity treatment using a convection oven or by use of visible or invisible light.
Conductive inks are materials that are particularly useful in printed electronics as electrodes and connections between components. Conductive inks are, in some ways, incompatible with printed electronics because they must be cured at relatively high temperatures (typically ˜80° C. or more), which may be detrimental to other materials useful in printed electronics.
Therefore, improved curing processes are desirable in the printed electronic industry. Moreover, a technique that cures printed materials, including conductive inks, while minimizing the amount of heat diffused to adjacent materials of a printed electronic device would be desirable, as it would significantly enhance the compatibility and use of conductive inks with printed electronics.